Compressed Air Foam Systems (CAFS) have recently gained popularity with many different types of firefighting organizations. The reason is simple. Foams are more effective in both putting out and controlling the spread of most fires. Foams are also cheaper to use than simply dousing a fire with water and also save the building owner a considerable amount in water damage. Also foams come in many classifications which work efficiently against all of the common types of fires.
One problem which has been of great concern to users of CAFS is the creation of turbulence in the delivery line at a point just downstream of the air injection port. Since air must necessarily be injected into the line at some point to ensure proper expansion of the foam, the problem of turbulence needed to be solved, since the delivery of the foam was impeded due to energy loss.
All previous attempts at solving the turbulence problem failed to some degree. These attempts included air injection at right angles relative to the water/foam flow, air injection at oblique angles, and mixing in various so-called motionless mixers such as the labyrinth, the perforated plate, the orifice and the modified orifice. While these mixers reduced the turbulence in the line, significant energy loss still occurred with the resulting loss of pressure and throw distance at the nozzle end.
More information about the general principles of CAFS can be found in the attached report of the U.S. Department of Agriculture.